Sandy Shalewing

The patterns on the wings of that creature resemble sand flowing through an hourglass. One could gaze upon them for ages...

Riding Requirements:

This mount is available to all eligible characters on your account.
Level 10
Apprentice Riding (ground)
Expert Riding (flying)

Source:

Achievement: Master of the Turbulent Timeways

Notes:

The Sandy Shalewing is only achievable during "Turbulent Timeways", which is a special Timewalking event in which five different sets of Timewalking dungeons are available over five consecutive weeks.

To obtain this mount:

Run four Timewalking dungeons on one character for each of the five weeks of the event.
Each Timewalking dungeon should award your character one stack of the experience buff Knowledge of Timeways. As this buff only lasts two hours you need to complete the next dungeon in less than two hours after completing the previous one.
Gaining four stacks of Knowledge of Timeways on one character will grant you the Mastery of Timeways buff. This is all you need to do for that week.
Repeat this each week, for the five weeks of the event. It's likely you can complete the weekly requirement on different characters in different weeks (as the achievement is account-wide), but this hasn't been tested.
After you gain Mastery of Timeways for each of the five weeks you'll complete the achievement, Master of the Turbulent Timeways and receive the Sandy Shalewing!